1. Field of the Invention
The invention relates to bone plates. More particular, the invention relates to bone plates and accompanying screws for repairing irregularly shaped bones such as the clavicle.
2. Description of the Related Art
Clavicle fractures account for approximately 2-5% of all fractures in the U.S. The majority of these clavicle fractures (approximately 75%) are located in the middle third of the clavicle, a very small percentage (<5%) in the medial third and the remainder in the lateral (or distal) third of the clavicle. Clavicle fractures have traditionally been treated non-operatively, even when one the fragments is substantially displaced. Clavicular nonunion was thought to be rare and of no clinical significance. Recent studies of displaced midshaft fractures of the clavicle, however, have shown a nonunion rate of 15% as well as a 31% unsatisfactory patient-oriented outcome. These statistics were published recently in the study entitled Nonoperative Treatment Compared with Plate Fixation of Displaced Midshaft Clavicular Fractures. A Multicenter, Randomized Clinical Trial in The Journal of Bone and Joint Surgery (JBJS) in January of 2007. The results of the study illustrate that primary fixation using plates is the recommended course of action for displaced midshaft clavicular fractures in adult patients.
Another type of clavicle fracture requiring plating occurs when the clavicle is not only broken and displaced but when a second fracture occurs causing a completely separated fragment. This condition causes even greater displacement and more patient discomfort and deformity if treated by non-operative procedures.
The clavicle is an irregularly shaped bone that provides the skeletal support for the shoulder. An intact clavicle forces the shoulder outward and backward. When the clavicle is fractured, muscle and soft tissue forces are now unopposed and this often results in the ends of the clavicle displacing (or telescoping inwardly) and rotating relative to one another as the shoulder drops and rotates forward. These forces make it difficult to realign (or reduce) a fractured clavicle so that a bone plate can be properly applied. The surgeon must pull the ends apart and rotate them back into position and must maintain this reduction while the plate is being secured.
The complex shape of the clavicle makes it difficult for a surgeon to bend a flat plate in surgery to match the many contours of the bone. The relative prominence of the clavicle however, requires that an implanted plate have as low a profile as possible, particularly on the ends where it transitions to the bone.
Most of the orthopedic plates and screws that have been approved for use in clavicle repair utilize plates designed for use in other areas of the body and on other bones which have a more uniform shape such as typical long bones. The typical long bone is characterized as being longer than it is wide, having a central shaft and two bulky ends and an inner medulary cavity. Bones of the leg, arm, hand and foot are the classic examples of long bones. These bones have a generally cylindrical shaft with far less curvature than would be found on a clavicle or a mandible. Plates designed for a typical long bone do not fit the more complex contours of the clavicle bone and present a number of problems in fixing the plate to the bone in an acceptable manner. Many of these plates are difficult to bend in general and are particularly difficult to bend at the ends of the plate—exactly where precise adaptation to the clavicle is desired. The shape of the clavicle requires the ends of a flat plate to bend and twist in three dimensions for accurate adaptation to the bone surface. The difficulty in doing so with a traditional long bone plate requires an unwanted expenditure of time and effort in the operating room particularly in light of the difficulty of reducing a displaced clavicle and maintaining that reduction.
A plate has been designed specifically for the clavicle. It is precurved in an “S” shape when viewed from above. While this precurvature generally mimics the profile of the clavicle, studies show that the variability in clavicles results in an inaccurate fit on clavicles in more than half the cases. Moreover, the study only examined two dimensions and did not account for the curvature and twist of the clavicle surface in the third dimension. The prior art S-shaped clavicle plate is flat in the third dimension and the plate is extremely thick making it very hard to bend in order to have the ends follow the surface of the clavicle.
Prior art bone plate designs suited for typical long bones include Huebner (U.S. Pat. No. 6,001,099), which teaches a bone plate with varying rigidity designed to prevent refracture of a bone adjacent to the end of the plate. The plate has essentially uniform thickness over the entire length, with a continuous curvature of the underside that relies upon the combination of varying width and spacing between plate holes to produce the desired reduction in stiffness as one moves from medial to lateral on the plate. Huebner teaches that such plates are particularly adapted to long bones such as those found in the leg, arm hand and foot. The cross-section of his plate is quite similar to that of Sherman (U.S. Pat. No. 1,105,105) in that it has the “concavo-convex cross section” which produces an increase in strength and stiffness over a generally rectangular cross section of the same width and thickness. While this may be applicable to typical long bones with a generally cylindrical shaft, the plate does not provide the needed three-dimensional contourability at its ends nor the reduced profile necessary for a complex and irregular bone such as a clavicle or a mandible.